1. Field of the Invention (Technical Field)
The present invention relates to targets and clamps for physical vapor deposition and similar processes.
2. Background Art
Information on physical vapor deposition and other similar processes are available from a wide variety of sources. For example, the Institute of Advanced Manufacturing Sciences (1111 Edison Drive Cincinnati, Ohio 45216-2265) provides such information to the public, for example, through its Web site (www.iams.org). The goal of most PVD and similar processes is to form a layer of material on a substrate. The formed layer is often referred to as a coating. In general, PVD coatings are between approximately 2 microns and approximately 5 microns. PVD processes encompass several different types of deposition processes in which atoms are removed by physical means from a source and deposited on a substrate. For example, processes that use thermal energy and/or ion bombardment are PVD processes that convert a source material into a vapor, which can later condense on a substrate. Thus, PVD processes typically involve evaporation of a first condensed phase to form a gas or vapor phase. The gas or vapor phase is then transported to or otherwise brought into contact with a substrate. The gas or vapor phase then condenses on the substrate to form a second condensed phase. It is important to note that the first and/or second condensed phases optionally comprise a solid phase and/or a liquid phase.
In a typical PVD process a substrate or xe2x80x9cworkpiecexe2x80x9d is placed in a vacuum chamber and a very high vacuum is drawn. The vacuum chamber space is heated to between approximately 400xc2x0 F. and approximately 900xc2x0 F., depending on the specific process. Where plasma etching is used, plasma is created from an inert gas such as argon to further clean the surface of the workpiece. Next, the source or coating metal is forced into a gas or vapor phase.
Three methods of forcing a source metal, alloy or compound thereof are commonly used: evaporation, sputtering, and ion plating. Evaporation comprises use of a high-current electron beam or resistive heaters to evaporate source material from, for example, a crucible. The evaporated material forms a cloud that fills the deposition chamber and then condenses onto the substrate to produce the desired film. In such a process, atoms take on a relatively low energy state (0.2 to 0.6 eV) and the deposited films, as a result, are not excessively adherent or dense. In some instances, deposition of a substantially uniform coating may require complex rotation of the substrate since the vapor flux may be localized and directional.
Sputtering is another method wherein the surface of the source material is bombarded with energetic ions, usually in an ionized inert gas environment comprising, for example, argon. The physical erosion of atoms from the coating material that results from this bombardment is known as sputtering. The substrate is positioned as to intercept the flux of displaced or sputtered atoms from the target. Sputtering deposits atoms with energies in the range of 4.0 to 10.0 eV onto a substrate. While sputtering is, in general, more controllable than evaporation it can be a rather inefficient way to produce vapor. For example, energy costs for sputtering processes are typically 3 to 10 times that of evaporation processes.
Another method is ion plating, which can produce superior coating adhesion by bombarding the substrate with energy and during deposition process. In ion plating processes, particles accelerate towards the substrate and arrive with energy levels up to hundreds of electron volts. These atoms sputter off some of the substrate material resulting in a cleaner, more adherent deposit. This xe2x80x9ccleaningxe2x80x9d process continues as the substrate is coated. The film growth is assured when the deposition rate is faster than the sputtering or cleaning rate. In general, high gas pressure results in greater scattering of the vapor and a more uniform deposit on the substrate.
An important variation on these processes involves the introduction of a gas such as oxygen or nitrogen into the chamber to form oxide or nitride deposits, respectively. These reactive deposition processes are used to deposit films of material such as titanium nitride, silicon dioxide, and aluminum oxide.
Overall, PVD processes results in a thin, uniform coating that is much less likely to require machining after application. The specifics of the aforementioned three variations of PVD processes are by no means exclusive. For example, some PVD processes use laser ablation or pulsed laser deposition to release a controlled amount of target material in the form of a gas. Also consider that accelerated plasma can be used in the PVD process to deliver a heat pulse to a target to release a controlled amount of gaseous target material.
Physical vapor deposition, and similar deposition processes are used, for example, in the fabrication of thin film materials, such as, but not limited to, fabrication of thin films for xe2x80x9ccompact discsxe2x80x9d (CDs). For example, sputtering processes are often involved in the coating of a semiconductor wafer or other substrate mounted within a processing chamber. In a typical semiconductor manufacturing, sputtering process, an inert gas is introduced into a processing chamber containing a target and an electric field is applied to ionize the inert gas. Positive ions of the inert gas bombard the target material and dislodge atoms from the target, which are subsequently deposited onto the wafer or other substrate in the form of a thin film. In many instances, the target is held within the deposition chamber by a device called a sputter-coating source. Often, the sputter-coating source has an electrical circuit for biasing the target material structure with a negative voltage, either DC for conductive targets, or AC having a radio frequency for non-conductive targets, so the target will attract positive ions from the plasma of an inert gas. To cool the sputter-coating source, a cooling circuit is often provided for the target structure. In addition, magnetic fields are useful for containing and enhancing the plasma.
In a semiconductor manufacturing, sputtering process, positive ions extracted from the plasma are accelerated to a high kinetic energy. These high kinetic energy ions strike the surface of the target structure whereby a portion of the kinetic energy is transferred to the target atoms of the target or source material. Target atoms that obtain sufficient energy to overcome their respective binding energy escape from the target surface and are ejected into the vacuum chamber. Objects, such as a substrate or a semiconductor wafer, placed in the line-of-sight of the target source are then coated by the atoms ejected from the target surface. Of course, it may be possible to xe2x80x9cbendxe2x80x9d the line-of-sight through application of electromagnetic and/or other energy.
In the prior art it is common to bond the metal or metal alloy target to a copper backing plate. An indium-based bonding technology is generally used to attach the target to the backing plate. The backing plate is required in order to support the target in the chamber in which the sputtering takes place. Often, materials used to bond the target to the backing plate contribute to contamination during the deposition process. In addition, bonding materials can interfere with the maintenance of electrical and/or thermal conductivity of the backing plate and the target. The deficiencies are dependent on the type of bonding material used; however, to date no single bonding material has emerged that does not introduce some process limitation. For example, some bonding agents have operating temperature restrictions. If the temperature of the bonded source exceeds a temperature restriction, then the bond may break and/or bonding material may enter the gas or vapor phase and consequently deposit onto a substrate. Therefore, a need exists for better bonding technology and/or altogether elimination or drastic minimization of the need for bonding material.
Note that the following discussion may refer to a number of publications by author and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
In a preferred embodiment, the present invention comprises a target assembly for PVD and similar processing equipment comprising at least one target and a clamp wherein the clamp clamps the target to the processing equipment. The present invention however is not limited to clamping, but rather, it encompasses attaching a target to the processing equipment with a component referred to herein as a clamp. In alternative embodiments, a clamp of the present invention is attached to the processing equipment through use of mechanical, chemical, metallurgical, electromagnetic, and/or magnetic attachment mechanisms. These mechanisms include, but are not limited to, welds, adhesives, ears, bolts and/or studs and the like. The clamp is optionally attached in a permanent manner to the processing equipment or in a removable manner. If the clamp is attached in a permanent manner, then it is preferred to provide a clamp comprising a mechanism for replacement of a target.
Stainless steel is a preferred material of construction of clamps of the present invention. However, other materials, including non-metals, are suitable depending on the processing conditions. Such other materials are known in the art of PVD and similar processes.
In a preferred embodiment, the target assembly comprises a ring-shaped clamp. In such an embodiment, the ring-shaped clamp fits over a substantially hat-shaped target that comprises a brim. The thickness and/or shape of the brim preferably matches and/or conforms to the ring shape of the clamp. In a preferred embodiment, the clamp comprises a diameter greater than that of the target; however, it is possible to configure a target assembly according to the present invention wherein the target comprises a diameter larger than that of the clamp. In such an instance, it is preferred that the clamp comprises at least one diameter that matches a diameter of the target. Of course, the diameter of the target and/or clamp may extend only over an arc and not a complete circle. Where the clamp comprises a diameter larger than the largest diameter of the target, the portion of the clamp that extends beyond the largest diameter of the target is optionally used for attaching the target assembly to the processing equipment. For example, this portion optionally comprises an annular region comprising apertures and/or other points for attachment. Alternatively, or in combination with such embodiments, the annular region is attached to the processing equipment through chemical, metallurgical, electromagnetic, and/or magnetic mechanisms. For example, but not limited to, a lower surface of an annular region of the clamp is attached through weld and/or adhesive attachment mechanisms. In a preferred embodiment, the size and/or shape of the brim are chosen to maximize material available for PVD and/or similar processing. Thus, according to such an embodiment, the amount of target material in a brim is minimized with respect to the total amount of material in the target. However, brim size and/or shape must be sufficient to carry any pressure applied by a clamp in attaching the target assembly to the processing equipment.
In a preferred embodiment, a clamp of the present invention comprises at least one aperture for receiving at least one bolt, stud, ear and/or other attachment fixture that is preferably positioned on the processing equipment. According to a preferred embodiment, a clamp comprising at least one aperture comprises at least one aperture comprising at least a partially open side. In such an embodiment, the partially open side provides for reception of at least one bolt, stud, ear and/or other attachment fixture that is preferably positioned on the processing equipment.
In a preferred embodiment, a clamp comprises at least one slot for contacting at least one bolt, stud, ear and/or other attachment fixture that is preferably positioned on the processing equipment. In such a preferred embodiment, the slot optionally comprises at least one surface that is horizontal, inclined, grooved, declined and/or marked with surface indicia that optionally increase friction between the surface and an attachment fixture. According to this embodiment, at least one of the attachment fixtures, comprising, for example, bolts, studs, ears and/or other attachment fixtures, travels in at least one of the at least one slot.
According to a preferred embodiment, the target comprises a hat shape comprising a brim wherein the brim comprises an upper surface. Of course, the hat shape need not comprise a circular horizontal cross-section. In general, targets and/or clamps of the present invention comprise at least one horizontal cross-section wherein at least one of the horizontal cross-sections optionally comprises a circular, oval, ellipsoidal, and/or polygonal cross-section. Furthermore, a target optionally comprises a brimless xe2x80x9chatxe2x80x9d shape, for example, but not limited to, a cone with a portion from the point downward removed, e.g., a partial cone shape. In such an embodiment, the target comprises at least one sloped surface wherein a clamp optionally contacts at least a portion of that surface with an edge and/or a matching sloped surface. For example, a clamp comprising an inclined inner surface for receiving a sloped surface of a target is within the scope of the present invention. Where a brim is present, a clamp preferably contacts an outer and/or upper surface of the brim. In general, targets and/or clamps of the present invention comprise at least one vertical cross-section wherein at least one of the vertical cross-sections optionally comprises a circular, oval, ellipsoidal, and/or polygonal cross-section. For example, in a preferred embodiment, a ring shaped clamp optionally comprises a circular or annular horizontal cross-section and a vertical cross-section comprising two separate polygons.
The present invention optionally comprises a target and/or a clamp comprising threads and/or other locking mechanisms that are optionally machined into at least a portion of a matching surface of a clamp and a target. In such embodiments, the target and clamp are screwed and/or otherwise attached to each other.
In a preferred embodiment, a target assembly attaches to the processing equipment through rotation of the assembly about a central axis of the assembly. In alternative embodiments, the assembly is attached to the processing equipment through rotational and/or translational motion.
In a preferred embodiment, the clamp comprises at least one piece. A single piece clamp optionally comprises a single piece of material that is machined and/or cast. In an alternative embodiment, a clamp comprises a plurality of cooperative pieces. For example, but not limited to, two semi-circular ring pieces and/or a central ring to which additional cooperative pieces are attached. Of course, clamps of the present invention are not limited to ring-like or circular shapes.
According to the present invention, a target comprises a metal and/or other material useful in the manufacture of products by PVD and similar processes. In a preferred embodiment, a target comprises a metal such as, but not limited to, gold, silver, niobium, tantalum, platinum, palladium, rhodium, iridium, ruthenium, and osmium. Targets of the present invention optionally comprise an alloy and/or a metal compound. In a preferred embodiment, a target comprises a ceramic, such as, but not limited to, ceramics for manufacture of xe2x80x9cread-writexe2x80x9d CDs (CD-RW) and the like. Of course, targets comprising pure materials and/or a mixture of materials are within the scope of the present invention.
In a preferred embodiment, a target comprises a shape that promotes processing. For example, in a preferred embodiment, a target comprises at least one aperture wherein the at least one aperture is optionally a central aperture positioned on a central axis of the target. As known in the art, such a feature is useful for the production of DVDs and CDs. Of course, targets optionally comprise a variety of shapes; for example, a target optionally comprises at least one circular, oval, ellipsoidal, and/or polygonal cross-section. According to a preferred embodiment, a clamp comprises an opening for receiving at least one of an at least one cross-section of the target. Of course, clamps that comprise more than one piece optionally comprise at least one of an at least one cross-section of the target when cooperatively assembled. Of course, in alternative embodiments, a clamp need not necessarily comprise a cross-section that matches a complete cross-section of a target; however, at least a partial match is preferred.
The present invention also comprises an inventive method of using a target assembly with processing equipment. In a preferred embodiment, the inventive method comprises the steps of providing a target and providing a clamp for clamping and/or otherwise attaching the target to process equipment. Again, as stated above, attachment mechanisms include, but are not limited to, mechanical, chemical, metallurgical, electromagnetic and/or magnetic attachment mechanisms.
In a preferred embodiment of the method, the target, the clamp and/or the target assembly comprises a known mass. In a preferred embodiment, the method optionally comprises the step of operating the process equipment to diminish the mass of the target. Accordingly, the method optionally comprises the step of removing the target and/or target assembly from the process equipment and from the clamp after an operating step. An additional further step comprising determining the mass of the target, clamp and/or target assembly after an operating step is within the scope of the present invention.
In a preferred embodiment, the present invention comprises a method of using a target assembly comprising the steps of providing a target assembly of a known mass, clamping and/or otherwise attaching the target assembly to process equipment, operating the process equipment to diminish the mass of the target assembly, removing the target assembly from the process equipment, and determining the mass of the target assembly. Of course, sophisticated process equipment that comprises the ability to determine the mass of a target, clamp and/or target assembly without removal is within the scope of the present invention.
An objective of the method is to determine the amount of diminished mass of the target from operation.
A primary object of the present invention is to minimize the need for bonding materials.
A primary advantage of the present invention is that the need for bonding material is minimized and/or eliminated.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.